DESCRIPTION (Taken from the application): Primary total hip arthroplasties (THAs) are undergoing late failure in large numbers. Compared to that of primaries, the scientific basis pertinent to the special needs of revision surgeries is much less well developed. Impaction grafting with morselized cancellous bone (MCB) is one very promising and increasingly clinically popular approach to THA revision, but one whose key technical attributes have received little in the way of systematic laboratory investigation. In that procedure, cancellous bone is ground up into small morsels, and impacted at the surgical site to build up bone stock. Ideally, normal bone remodeling proceeds from the adjacent live host bone, into the bone graft, such that eventually the MCB graft is fused into a new cancellous lattice that is contiguous with the host bone. Despite widespread (and growing) use of impaction grafting with MCB in THA revision, effective use of such grafts has largely relied upon intuitive surgical judgement. Better bio-mechanical exploration with realistic bench/cadaver models should help optimize the procedure. Progress in this area has been hindered by inability to study the end-stage (i.e., totally fused) condition, rather than the immediate postoperative situation of non-cohesive MCB. Using a recently developed model of MCB fusion, this study will investigate bio-mechanical aspects of impaction grafting in cemented revision THA, spanning the time period from the immediate postoperative situation (non-cohesed MCB particles) to the final clinical target stage (fused MCB). The specific aims are to 1) extend development of the laboratory MCB fusion model, 2) measure the change in stability of impaction grafted revision THA prostheses, before and after MCB fusion, and 3) measure the change in stability of impaction grafted revision THA prostheses, when the MCB is fused only in certain regions. The research design will include the following: 1) creating cavitary defects in cadaveric femurs and acetabulae, 2) impaction grafting and implanting of cemented THA prostheses, 3) using a new laboratory MCB fusion model which allows the MCB particles to fuse, and the fused MCB to also fuse to the bone in which it is impacted, 4) loading the prostheses with a replication of the full physiologic load cycle during level walking, and 5) measuring prosthesis subsidence and micromotion. Successful conclusion of the proposed research will provide biomechanical data that will assist in the optimization of the impaction grafting process, thus improving the clinical success rate of this evolving procedure.